Internal combustion engines are used as the primary power plant for vehicles. An energy source such as gasoline or diesel fuel is used to cause expansion of fuel vapors or gases within cylinder chambers wherein pistons, connecting rods, and a crankshaft convert the pressure produced by the expansion into rotation movement. Control of the cylinder chamber is performed by sequential operation of intake and exhaust valves positioned into each chamber.
The valves are mechanically operated through a transfer of motion from a camshaft having eccentric oval shaped lobes. In overhead valve (OHV) engines, the camshaft lobes lift push rods which engage rocker arms mounted at the head of the cylinders. The rocker arms allow pivoting of the arm so as to rock up and down which in turn depress the biased intake and exhaust valve.
While this transfer of motion is effective, it does place a strain of the rocker arms and their related components during conditions of high torque such as when the engine is used for high performance applications including aircraft, automotive, marine, motorcycle and off-road use. During such use, even slight offset movement of rocker arm components may lead to incorrect tolerances multiplying efficiencies and causing burnt valves or possible cylinder destruction.
One such problem is the stud used for securing each rocker arm to the cylinder head. The typical rocker arm mounting stud is a steel threaded bolt used as the sole mounting device. A rocker arm can be secured to the stud with or without a means for adjusting operating clearances. A rocker arm design having adjustment ability will only control rocker arm loads from one direction while under load. However, when the rocker arm is in between operating cycles, and not underload, the rocker arm will "float" providing a lack of support to un-reciprocated component weight. A rocker arm design without adjustment is typically mounted in a fixed support position relying upon alternative methods of adjustment, such as the cam follower or hydraulic lifter, to provide a constant variable pre-load.
No device is known to combine the adjustability of floating rocker arms in combination with solid fixed mounts in the securement of the top and bottom of the rocker arm. The principle of the rocker arm retainment is to secure the rocker arm to the cylinder head limiting its upward motion at the pivoting point as retained by a single mounting stud that attaches to the cylinder head. Prior art single-stud designs are limited in attachment in a single direction, upward, away from the cylinder head and mounting stud and employ a single nut assembly atop the rocker arm for use as the locking device so as to securely attach the rocker arm to the mounting stud. This attachment allows the rocker arm to float when there is no upward load by the rotational action of the camshaft and its related components. There are two conventional design variations which affix the rocker arm to the cylinder head on a single stud mount design. The first design requires rocker arm adjustment. In such cases having a single rocker arm mounted to a single stud the design requires an adjustability of the rocker arm to provide for proper operating clearances to the related components thereby facilitating the adjustability of its installed height to the assembly of components. The second traditional design variation requires no rocker arm adjustment. In prior designs which have a single rocker arm mounted to a single stud for this operating method, the elimination of the need for adjustability for the rocker arm to provide for proper operating clearances rely upon a "bolt like" attachment to draw the rocker arm assembly down to a fixed and predetermined position whereby the required adjustability of the assembly of components is handled automatically by a hydraulic adjustment within a cam follower. This is also known as a lifter. In this type of design the rocker arm is pulled down upon a mounting stand that does not allow the rocker arms body to float as with the rocker arms that require providing a more permanently fixed attachment directly to the cylinder head. The hydraulic lifter does improve overall operation of the assembly but merely offers a decrease in assembly time by elimination of tolerance adjustment to the rocker arms. Thus, what is needed in the art is a rocker arm mounting stud which effectively combines adjustability with solid fixed blocking of the rocker arm to the cylinder head.
Still another problem with rocker arms is the pivoting action the rocker arm places on the mounting studs. Especially in high torque, high performance applications such as racing vehicles. In such application, demands are made that the rocker arm pivot point is maintained in a stable position. Misalignment of only a fraction of an inch can translate into incomplete operation of the intake or exhaust valve.
Attempts at increasing the rocker arm stability include the use of thicker castings which translates to heavier engines and heat dissipation problems. In single stud designs, a known device for stabilizing the upper end of the stud is a stud girdle. This device is secured by means of a horizontal clamping force placed around the stud mounting bolts by the use of straddling bars of metal, usually aluminum. The force is applied by simply coupling two or more adjusting nuts by use of a common bolt placed between them which would draw or tighten the two sides of the two piece girdle together. The result is a straddling of the adjusting nuts into a retained position by the use of clamping force.
The girdle is mounted on top of the rocker arm assembly, securely fastening to the rocker arm studs wherein deflection of one rocker arm stud is translated to the remaining rocker arm studs thereby strengthening and effectively eliminating any deflection. The problem with known stud girdles of the prior art is that by simply attaching a girdle to the rocker arm studs will not prevent stud deflection in all applications and may even lead to stud deflection if improperly installed. Further, it has been found that the use of stud girdles are ineffective in a number of high torque, high performance situations as the stud girdle typically comes in two piece sections that are required to be bolted together providing an area of expandability since the stud girdles use fasteners to hold the girdle together as well as incorporating the use of the studs to fasten the stud girdle to the cylinder head.
Thus what is needed in the art is a solid bar that applies a direct force between two or more studs in lieu of a girdle.
Another problem with rocker arms of the prior art is the metal on metal contact of a conventional non-roller rocker arm tip. Rocker arm designs without a roller tip are attached to the cylinder head in a number of ways to provide a reciprocal action to open the valves. Typically the roller tip rocker arm is mounted in a fashion so that its rotational motion is perpendicular to the linear path of the valve, providing a valve tip surface to have full contact across the width of the roller tip.
Numerous applications of American made overhead valve engines such as the 350 cubic inch "CHEVROLET" engine as well as the 302 and 351 cubic inch "FORD WINDSOR" engines have wedge combustion-chamber cylinder head designs wherein offset changes of the rocker arm between its mounting points to the head in the contact angle of the valve has introduced a misalignment of the normal rotational motion of the rocker arm. The misalignment has a significant increase in wear, thereby decreasing both longevity and performance. Prior known art to correct this situation has been to completely remachine the mounting angle of the rocker arm to the exact fraction of a third dimensional rotation. Alternatively, the rocker arm mounting system can be offset so as to keep the rocker arms access on a two plane rotational movement. Thus, what is needed in the art is a rocker arm providing a third dimensional rotation to compensate for misalignment.